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Electrical circuits

What should you know before starting this unit?

This unit is a continuation of Electricity. In that unit we already studied some basic concepts that you should remember:

  • What is an electric current?
  • How does an electric current flow through a circuit
  • What are electrical conductors and electrical insulators
  • The difference between the intensity and the voltage of an electric current.
  • The different ways in which several electrical components can be connected: series, parallel or series-parallel circuits.

Why do we study electrical circuits?

Probably, electricity is the only topic that you are going to study in each of secondary education courses, though each time with a greater degree of complexity. The reason why so much time is dedicated to this field is that the number of applications of electricity in our daily life is huge. Knowing how electricity works will allow you to understand how a lot of machines around you work and this way you will achieve a deeper understanding of the world you live in.

Electricity has played a fundamental role in our lives since more than one hundred years ago when we started to learn how to use it to improve our lives. If you have never thought about how our lives would change if suddenly electricity disappeared from our society I invite you to do it. Now I will show you some examples of devices that you will not be able to use if such thing happened.

  • Means of transport: some of the means of transport we use daily are powered by electricity:

But even in those vehicles that use some kind of fuel (gasoline, for example) electrical circuits are essential. This is the case of cars, motorcycles, planes… Thanks to electricity we are able to turn the engine on, turn on the headlights of a car, activate the wipers… Did you know that in a car like the one below (which is not an electric car) more than 2km of electrical wires are necessary? Now imagine the case of a plane, whose electrical circuits are responsible of tasks as important as controlling the autopilot mode:

  • Electronic devices: that’s it, communication with your friends and family would become much more difficult if we were not able to use electricity: smartphones, laptops, tablets…

But talking to other people and entertainment is just a very little part of the utilities of this kind of device. You can not even imagine how many tasks are carried out automatically thanks to computers nowadays: weather forecasts, stock records in warehouses, online shopping, robots in assembly lines…, though some times we forget, all of them work thanks to computers.

  • Lightning: you may think it is not that important, but can you imagine how dangerous it would be to drive your car in a city without traffic lights? Have you thought about how the number of crimes would increase if our cities lacked lights?
  • And many other applications that maybe are not vital but make our lives much more comfortable: lifters, home appliances (washing machines, ovens, fridges…), ATMS (Automated Teller Machine)…

What is, and what is not, an electrical circuit?

An electrical circuit is a group of several electrical components connected in such a way that the electric current that leaves the battery through one of its terminals (or poles) can return to it through the other terminal.

The images below show some basic components that we have already studied in the previous course. Do you remember them?

Metals are the electrical conductors that we use to make the electrical wires that join the components of a circuit. Wires can be made of copper, aluminum, steel, gold… you can remember it here.

The fact that the electric current of a circuit needs to find a way to go back to the battery is fundamental. Otherwise, we can not properly talk of an electrical circuit. Remember that a battery is a device that pushes electrons through the circuit, but if there is not a closed path for electrons to return back to it the battery will not be able to generate any electric current.

For example, though the two image below are very similar, one of them represents an electrical circuit while the other does not. Could you tell which one is an electrical circuit?

If your answer is the one on the right you are correct. Remember that the electric current leaves the battery through one of its poles, through the positive pole in particular (the red one), and returns to it through the negative pole (the black one). The path that the electrons would follow has been marked in blue. As you can see in the circuit on the left electrons are not able to find a way back to the battery (obviously they can not jump through the air), so we can not say the left scheme represents an electrical circuit. On the contrary, in the circuit on the right, electrons can follow two different paths back to the battery, so in that case we can say it is an electrical circuit.

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